Odds ratio - univariate and logistic regression points in different ways

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Contributor
Posts: 28

Odds ratio - univariate and logistic regression points in different ways

Dear anyone

I am using SAS 9.4, enterprise guid 6.1. I am looking at the risk of taking medicine X if you have symptom A, B and C. I have to groups: I Use of medicine X and II no use of medicine X. All symptoms are more frequent in the group that uses medicine.  When I do univariate analysis I get the following odds ratio for taking medicine X: 3.4, 2.3, and 1.2. When I do a logistic regression I get 0.3, 0.6 and 1.2

I can appreciate that I get something close to the inverse OR depending of my coding. But how can symptom C point in another direction than the rest. To me it does not make any sense. Can anyone please help me.

Se tables for details

Sincerely

Anders

Univariate
Symp A Total
01
med
0Frequency513144657
Row Pct78.0821.92
1Frequency287270557
Row Pct51.5348.47
TotalFrequency8004141214
OR=3.4
SympB Total
01
med
0Frequency548109657
Row Pct83.4116.59
1Frequency382175557
Row Pct68.5831.42
TotalFrequency9302841214
OR=2.3
SympC Total
01
med
0Frequency59859657
Row Pct91.028.98
1Frequency49760557
Row Pct89.2310.77
TotalFrequency10951191214
OR=1.2

Logistic regression
Odds Ratio Estimates and Wald Confidence Intervals
EffectUnitEstimate95% Confidence Limits
SympA 0 vs 110.3340.2570.435
SympB 0 vs 110.6270.4680.842
SympC 0 vs 111.1570.7711.734
Super User
Posts: 10,466

Re: Odds ratio - univariate and logistic regression points in different ways

Code used to generate the summary will be helpfule as there are enough options involved that just the output is not enough for diagnostics.

Contributor
Posts: 28

Re: Odds ratio - univariate and logistic regression points in different ways

Dear ballardw

Thank you for your answer. I sincrely appologize for my late reply. I have had some IT difficulties.

I have talked to a statistician and the 'problem' was just confounding.

Sincerely Anders

Super Contributor
Posts: 339

Re: Odds ratio - univariate and logistic regression points in different ways

My first haunch would be that you did not use the DESCENDING option in your proc logistic so it's modeling the odds ratio of going from state "taking the medicine" to "not taking the medicine"

Contributor
Posts: 28

Re: Odds ratio - univariate and logistic regression points in different ways

Dear Vince

Thank you for your answer. I sincrely appologize for my late reply. I have had some IT difficulties.

I have talked to a statistician and the 'problem' was just confounding.

Sincerely Anders

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